Effect of annealing on the structural and optical properties of heavily carbon-doped ZnO

ZnO films grown by metalorganic vapor phase epitaxy (MOVPE) at low temperatures (similar to 500 degrees C) exhibit very high levels of carbon incorporation in the range of up to several percent. Such large levels of carbon incorporation significantly affect the structural properties of the thin films resulting in broadening of symmetric (0 0 2) rocking curves as well as broadened (1 0 1) pole figures compared with films grown at high temperature. Annealing of the films under air ambient at temperatures between 800 and 1100 degrees C results in dramatic sharpening of symmetric (0 0 2) rocking curves, indicating improved crystal alignment along the c-axes. (1 0 1) pole figure scans also show significant sharpening in the azimuthal axis, indicating similar improvements in the in-plane crystal alignment perpendicular to the c-axis. Raman spectra for as-grown ZnO at 500 degrees C show strong D and G peaks at 1381 and 1578 cm(-1) due to sp(2) carbon clusters. Annealing at 1000 degrees C results in the elimination of these bands, indicating that post-growth annealing treatment is a useful method to reduce the concentration of sp(2) carbon clusters.